Electrolytic process



United States Patent ELECTROLYTIC PROCESS Stuart 5. Carlton, Cleveland, and Bertram C. Raynes, Euclid, Ohio, assignors, by mesne assignments, to Horizons Titanium Corporation, Princeton, N.J., a corporation of NewJersey No Drawing. Application July 9, 1956 Serial No. 596,450

12 Claims. (Cl. 20464) This invention relates to the refining of impure titanium metal and its alloys by an electrolytic procedure. More particularly, it relates to a method of electrolytically refining impure titanium material in a fused salt medium by passing a direct current between a cathode on which a refined titanium pro-duct is deposited and solid impure titanium immersed in the fused salt and in electrical contact with an anode.

Titanium metal and titanium alloys have recently achieved considerable prominence as materials of construction possessinga peculiarly advantageous combination of properties. The relatively low weight and excellent corrosion resistance to particular environments have caused this metal and its alloys to be employed in a number of applications with outstanding results.

Most of the titanium presently producedis obtained'by the reduction of titanium tetrachloride by means ofrnagnesium as in the Kroll process, described in U.S. Patent 2,205,854 or by means of sodium or other reducing agents. The resulting product, after treatment to remove various contaminants, is then consolidated by are melting or other techniques.

In another approach to the production of this metal, the metal is recovered from various titanium compounds by electrolysis of fused salt baths containing titanium compounds. Thus, the production of titanium metal in the from of a cathode deposit from a fused bath by the electrolytic decomposition of titanium monoxide is described in U.S. Patent 2,707,168. Electrolytic decomposition of a mutual solid solution of titanium monoxide and titanium carbide is disclosed in U.S. Patent 2,722,509. The decomposition of purified alkali metal fiuotitanates is taught in U.S. Patent 2,731,402. The production of titanium from various other titanium compounds, principally titanium halides, is disclosed in a number of other U.S. patents, but except for metal produced by the De Boer-Van Arkel (iodide) process, it has been found necessary to separate the metal produced by pyrometallurgical processes from other contaminating reaction constituents. In addition, titanium produced by pyrometallur- .gical process always contains a proportion, sometimes large, of off-grade impure metal unsuitable as primary metal.

Furthermore, in the fabrication of the titanium metal and its alloys, a high percentage of scrap material'is generated in the form of bar, sheet and ingot croppings; turnings and shavings; and material of even finer particle size from grinding, drilling and boring operations. Be cause of the high affinity of the metal for oxygen and nitrogen, the reclamation of the scrap material by simple melting procedures has been found to be diflicult. Furthermore, ,much, of they scrap already ,containssubstantial proportions of tenaciously held impurities acquired either during'the'initial winning of the metal or .during the subsequent conversion of the :metalato various finished products.

2,880,149 rateateaMaa-ei, 1959 ice Unfortunately, in many of the foregoing procedures the metal scrap or the crude virgin metal obtained after'removal of adhering salts is contaminated with oxygen and/ or other impurities which severely restrict its utility and cause its properties to be noticeably impaired.

In British Patent 728,523 which appears to correspond to United States Patent 2,734,856 there is described a method of refining impure titanium metal in which impure titanium metal formsthe anode in a fused salt electrolyte comprising titanium .dichloride'and titanium trichloride in stated concentrations. Whenproceeding in the manner described in the British patent the metal product obtained as a cathode deposit usually had a Brinell hardness of 200 or more which greatly-exceeded the hardness which was acceptable to the'trade. 'By suitably'modifying the process-it has now been discovered ,that when crude titanium metal or titanium scrap,,both

alloyed and unalloyed, is electrolyzed in a fused salt bath in the manner about to be described, the metal obtained as a cathode deposit has a Brinell hardness lower than 120 and often as low as -90, and is substantially free from the major portion of these undesirable contaminants. This metal has-a usefulness'greatly exceeding that of the unrefined metal and it has been found that the metal may be consolidated directly into solid stock material by suitable powder metallurgical technique, thus avoiding the necessity for melting the product metal to obtain useful product, as has been heretofore necessary in the utilization of titanium produced by electrochemical or pyrometallurgical techniques.

Briefly, the method comprises electrolysis of a fused alkali metal halide salt bath containing an alkali metal fluotitanate as a carrier salt in which there is immersed titanium metal or titanium alloy scrap which is in electrical contact with an anode, the electrolysis being carried-out under certain conditions about to-be described, which have been found to be determinative of the quality ofthe metal produced. It has been found that the electrorefiningof the impure metal produces, aftera short time, dependent uponthe impurity vand alloy content of the metal, a sludge containingsubstantially all of the nonmetallic contaminants and a portion of the metallic contaminants in addition to some of the titanium metal content of the material to be refined.

By maintaining the over-all cell voltage and theanode current density at values below those at which the sludge exhibits any appreciable tendency to go into solution in the fused bath, particularly when in contact with a supply of available metal and maintaining a fresh, supply;of available titanuim scrap in the cell at at times and in electrical contact with the anode and with the fused salt bath and particularly with the sludge, it has been found that oxygen, hydrogen, nitrogen, carbon and other nonmetallic impurities are not transported to the cathode or deposited thereon. As a result, the cathode deposited metal is considerably purer than the material to be re fined.

While we do not wish to be bound by any specific theory as to the reasons for the much lower'hardness of the metal obtained by the changes introduced by us in the process described in British Patent 728,523, we believe that in the vicinity of the anode the metallic titanium,:in the form of the impure material to be refined, at the elevated temperatures at which the electrolysisis to be carried out,-appears to function as a getter or seques- In carrying out the process, a melt is prepared by fusing a mixture of alkali metal halide salt and alkali metal-titanium double fluoride. To the fused melt, there i is then added the impure titanium metal. One or more of several possible reactions is then believed to take place, whereby a titanium carrier in which the titanium is trivalent or possibly divalent forms. The formation of such a material may follow from either a chemical reaction (e.g. 3Ti+ +Ti- 4Ti+ or an electrochemical reaction (e.g. Ti+ +e Ti or both; that is, it may occur before any electrical current is passed through the cell or as a result of the passage of such current, or partially from both causes. In any event, in order to electrodeposit pure titanium metal at the cathode, a carrier ion in which the titanium has a valence less than four is required to be present in the fused salt bath.

Regardless of the actual explanation, we have found that in continuous cell operation the purity of the cathode deposited metal, as evidenced by the diminished hardness and increased purity of such metal, and the efficiency of the electrolysis, were both noticeably increased whenever an excess of metal was present in the region of the anode, and when an excess of such metal was in electrical contact with any sludge present, as would be the case, for example, immediately after compacting the charge and immediately after charging a fresh supply of metal to be refined, into the cell.

The fused salt bath in which the present electrorefining is effected is preferably formed of a solvent comprising one or more alkali metal halides and one or more of the normal double fluorides of titanium and an alkali metal. The alkali metal halides are available commercialy of a purity sufficient for the present process. For reasons of economy, the akali metal chlorides, particularly sodium chloride, are preferred, but any of the other alkali metal halides may be used, either alone or as mixtures of one or more of said halides. Preferably the alkali metal halide is in the anhydrous condition. Double fluorides of the alkali metals and titanium are also available commercially, particularly K TiF and Na TiF As has been indicated in US. Patent 2,731,402, it is desirable to subject these double fluorides to at least a simple recrystallization, to remove most of the extraneous impurity content and thereby to improve the quality of the metal obtained. It should be understood that such a treatment is optional, and is preferred because it tends to diminish the total amount of sludge formed during the electrolysis.

A preferred anhydrous salt bath electrolyte composition useful at the start of a refining operation is one containing about 16% by weight of K TiF and about 84% by weight of NaCl. The process may, however, be operated with as little as 3% or as much as 30% by weight of the double fluoride in the initial fused electrolyte. To lower the cost of the bath ingredients, it is preferred to operate with no more than 18% of the double fluoride in the fused salt electrolyte. Under the usual conditions of operation, the bath composition remains virtually unchanged during the operation, and it merely becomes necessary to add make-up salts from time to time to compensate for the mechanical losses or for salt removed with the cathode deposit. The make-up salt addition is preferably in the form of a mixture of NaCl and K TiF in the ratio of 84:16 by weight.

The other major raw material in the process is the impure titanium metal. As has been indicated above, this may be either virgin metal, such as that obtainable by the Kroll process or other processes, or scrap metal produced as a result of normal fabrication of the metal and its alloys. When the metal is grossly contaminated with dirt, grease, or other undesirable material (e.g. masking tape) it is cleaned by any'of the conventional methods common in the treatment of scrap, e.g., by tumbling the scrap in contact with a solvent such as trichlorethylene.

Depending on the configuration of the cell, it may be found to be necessary to reduce the titanium scrap in size or to consolidate by bundling, pressing, etc., before any refining is performed in the electrolytic cell.

The electrolytic cell employed in the process consists of a container of any suitably refractory material. Graphite, nickel, iron, stainless steel and other alloys have been found suitable as the crucible or container. In the manner now well known in this art, the cell should be provided with means to heat the contents and to maintain the contents molten; means for maintaining an inert atmosphere in the cell; and a diaphragm or bafile for confining the scrap charge to a region adjacent the anode. The container itself may advantageously serve as the anode.

The electrolytic cell thus consists of a container, means to heat the container, means for maintaining any desired inert atmosphere therein, at least one cathode suspended in an electroylte contained in the cell, at least one anode in the cell, and means whereby the impure charge is confined, within the melt, to a region closely adjacent the anode.

The metal added to the melt is added adjacent to the anode and remote from the cathode. Preferably it is confined to the regions of the cell which are farthest removed from the cathode. For instance, in a cell in which the bath is contained in a square or rectangular crucible, and with the cathode suspended at the intersection of the diagonals, the scrap is confined to the corners of the anodic crucible by means of perforated bafiies of graphite or other suitable metallic or ceramic material.

When graphite is used as one of the materials of construetion of the cell or baffles, or when pieces of graphite or of titanium carbide are added to the charge, we have found that the sludge formed during the refining operation consists principally of a compound having the formula Ti OC.

When the anode (crucible) has a circular cross section, e.g. when it is cylindrical, with the cathode suspended along the axis of the cylinder, the scrap-confining means may conveniently comprise a perforated cylinder of smaller diameter, nested in the larger cylinder. For other cell geometries, other arrangements will be readily apparent to those skilled in the art.

Before the cell is heated, an argon, helium or other suitable inert atmosphere is provided. Thereafter the electrolyte and scrap charge are heated and electrolysis is initiated following the charging of the scrap. Electrolysis proceeds smoothly at cathode current densities of between and 600 amperes per square decimeter, and at bath temperatures between about 875 C. and 950 C. No significant evolution of gas occurs once the cell is operating properly. From the wide range of cathode current densities at which the process has been operated satisfactorily, it will be readily apparent that the cathode current density is not a critical operating limitation. Rather, we have found that in the present process, the anode current density is of much greater significance in determining the quality of the refining achieved. Since the cathode dimensions are continually increasing during electrolysis, it would be difficult to maintain any exact current density, but this situation does not obtain at the anode, which retains its original average geometric dimensions throughout the process. Hence operation at a specific anode current density is relatively easier to accomplish. In our process, anode current densities of 7-75 amp/sq. dm. have been found to produce satisfactory metal while densities in the range 35-40 amperes per square decimeter, have been found to produce optimum refining of the impure metal.

The following examples will serve to further illustrate our invention but are not to be taken as limitative thereof.

EXAMPLE I After an electrolytic cell with a dry argon atmosphere -T he cathode was about 3% inches fromthe anode.

-5 4 was heated to a temperature of about 850."C., commercially pure sodium chloride was charged into'the cellv and heating was continued under the argon atmosphere until the sodium chloride was fused. Recrystallized potassium fluotitanate was charged into the fused sodium chloride in the proportion of 6 parts of K TiF to 84 parts of NaCl (by weight). Pieces of degreased metallic titanium scrap in the form of small clippings approximately /2 inch x inch in area and V inch thick were charged between a perforated graphite barrier which served as the anode, and the crucible wall, which was also anodic. The scrap was tamped witha tamping rod to insure thatit would remain in physical contact with the. anode and withany sludge formed during the electrolysis. An iron cathode was then inserted into the bath to a depth of 9 inches. The cell temperature was maintained between about 910 C. and 935 C. and electrolysis of the charge was carried out at this temperature under the argon atmosphere while maintaining the cell voltage within the" range of 2.8' and 2.9 volts. The cathode current density during the electrolysis period of 110 minutes varied between 225 and 450 amperes per square decimeter, and the anode current density varied between 34 and 39 amperes per square decimeter. After 1710 ampere hours had been passed through the cell, the deposit was withdrawnystripped from the cathode and separated from adhering salts. To

initiate further runs, the cathode was reinserted into the 16 The unrefined scrap analyzed, in addition to titanium:

Percent by weight Not detected-Cd, Sb, B, Pb, Co.

Results of refining this scrap by electrolysis under an argon atmosphere, in. a K TiF NaCl fused salt bath, at temperatures between 890 C. and 930 C. and anode current densities within the range of amperes per square decimeter and amperes per square decimeter of anode area are shown in Table II.

Table II Metal Brinell Percent Percent Percent Percent Hardness H N C T able I A more complete spectrographic analysis of the products ofsome of the runs in Example I and Example II Metal Brinell Percent Percent Percent Percent; i i

Hardness O H N .0 S glven below 218 0.233 M32 M16 M14 Run VII-3 RunvIIr-5 Run X-75 RunXI-14 s3 0. 020 0. 000 0. 009 107 0.015 0. 002 0. 002 0. 023 gfif 0 %s 0 23 05 05 05 0. 050 0. 001 0; 005 0.009 0 609 01 0. 077 0. 004 0. 002 0. 005 0 605 0 b0? 94 0. 043 0. 002 0. 005 0. 014 003 004 003 it; 8833 3882 8'83 0103 0104 @004 11s 0I073 01000 01014 82 8'82? 8832 0.001'each Mo, V, Ni Sn, Cu 107 M24 50 Not detected-Cd, Sb, is, P, on.

A spectrographic analysis of the originalscrap showed the. following in addition to titanium:

'EXAMPLE II Example I was repeated'using a scrap comprising chips about /2 inch x 1 inch in size, produced in amachining operation. The scrap was a uniform golden-color and was charged into the cell in theas received conditiomit having been degreased before shipment.

EXAMPLE III -A synthetic titanium scrap was made by heating forty pounds of' the scrap of Example I to temperatures between 1200 and 1400 C. in the presence of controlled amounts of air. The resulting product was separated intoa silvery-gold fraction (I) and a blue to violet fraction (II). Both fractions were electrolyzed in the same manner as in the previous examples in a fused (84:16) melt at about 900 C. and at 1.5-2.8 volts, and 35-40 amperes per square decirneter of anode area.

The results are given below.

Table III Metal 7 Brlnell Percent Percent Percent Percent Hardness O H N 0 1 EXAMPLE IV Efforts made to refine the scrap of Example I by repeating the procedure of that Example except that the scrap was not tamped to squeeze out the sludge formed in the main body of the anode and to maintain the bottom part of the scrap in contact with the sludge which formed, resulted in products with Brinell hardness considerably in excess of 120, and often as high as 250 or higher. It was found that immediately after tamping the scrap, the hardness and purity of the titanium product were greatly improved as compared with the hardness and purity of metal produced just previously thereto. The following consecutive runs, made under process conditions which were substantially identical except for the disposition of the scrap, illustrate this point.

Table IV Brinell Remarks Hardness 238 Tangled, 20 pounds of scrap ad ed. 180 159 205 Scrap tamped, 12 pounds of scrap added. 160

250 235 Tamped, 12 pounds added. 195 Tamped, 12 pounds added.

As seen from the preceding description, impure titanium metal has been refined to a product which is a high purity ductile titanium, by passing a direct electric current through a fused salt bath consisting essentially of at least one alkali metal halide and at least one double fluoride of titanium and of an alkali metal, maintained at a temperature of about 920 C., and under an inert atmosphere, and by maintaining the impure metal disposed in a manner in which dissolution of the sludge formed was not favored.

An X-ray diffraction analysis was performed on the water insoluble part of two sludges recovered after 73 electrolytic runs and 94 electrolytic runs respectively. The results indicated the presence of carbon and of titanium oxycarbide, a solid solution of TiO and TiC approximating the formula: Ti OC. Neither free titanium metal nor titanium oxides could be identified. Petrographic examinations indicated the existence of only two phases: carbon and titanium oxycarbide. For the later series of runs, the proportion of Ti OC:C was much higher than for the earlier series, showing that the compacting or tamping of the loose scrap tended to force the sludge out of the scrap material, whereby fresh scrap surfaces were presented for electrorefining.

Metal powder recovered from the cathode deposits of typical runs was mixed, briquetted and arc-melted into cast buttons. Each of the buttons was cold rolled 40% from an original thickness of 0.475 inch. The cold rolled product was annealed at 700 C. and reduced another 40% by cold rolling. The strips were again annealed at 700 C. and cold rolled to 0.063 inch thickness. The product strip was ductile with a good surface and very little edge cracking. The total reduction was 87%.

Samples of the 0.063" strip were tested for tensile properties. The tensile strength was found to be 115,000 p.s.i., the elongation 12% and the hardness of the as rolled strip was 245 Brinell. When annealed at 750 C. for one hour the hardness of the strip fell to 125, the percent elongation increased to 34% and the tensile strength was 52,000 p.s.i. Furnace cooling after the anneal at 750 C. produced a product with a 64,000 p.s.i. tensile strength and a 30% elongation, properties comparable with those of commercial titanium. The annealed strip had a fine grained equiaxed alpha structure, characteristic of pure titanium.

Other metal powder recovered from the cathode deposits of typical runs was cold briquetted into compacts 1 inch in diameter and about 2 inches in thickness. The compacts were made by pressing at about 25,500 p.s.i. and had green densities of between about 2.6 and 3.2. After heating in an argon atmosphere the compacts were extruded to /4 and diameter rods, at reduction ratios of 16/1 and 7/1 respectively, at a temperature of about 1400" F. Tensile tests were performed on two of the extruded rods with the following results, after annealing for one hour at 750 C.

Table V Percent Tensile Elong- Dlameter BHN Density Theorct- Strength, tlon,

lcal p. s. 1. percent Density 'amounts of oxygen, carbon, sulfur, nitrogen, or more than one of these elements, and metallic compounds of titanium, e.g. ferrotitanium are suitable raw materials in our process to recover titanium in the form of a cathode deposited pure metal. Furthermore, although for the sake of brevity the description has been confined to a discussion of the refining of titanium bearing material, we have found our process to be equally applicable to the treatment of materials containing other elements in Group IV-A, particularly zirconium and hafnium, to produce said elements substantially pure metals, in the form of cathode deposits from a fused salt electrolysis as above described.

We claim:

1. The method of electrolytically refining impure titanium metal to produce a refined ductile metal having a Brinell hardness number less than which comprises: providing an electrolytic cell having an anode and a cathode with an inert atmosphere, and a molten salt electrolyte consisting essentially of at least one alkali metal halide and at least one alkali metal fiuotitanate; maintaining said atmosphere inert and said salt molten; charging impure titanium metal into said molten salt so that it is in physical contact with said anode; passing an electrolyzing direct current through said cell thereby depositing titanium on said cathode and forming a sludge containing the impurities in said impure metal; maintaining said sludge in physical contact with the unrefined impure titanium metal; maintaining an anode current density and voltage during the passage of said current sufficient to deposit purified titanium metal at the cathode but insufficient to liberate any halogen gas at the anode and insufficient to electrolytically dissociate any of the sludge formed during said refining; thereby separating impurities from the titanium metal and depositing refined titanium at the cathode.

2. The method of electrolytically refining impure titanium metal to produce a refined ductile metal having a Brinell hardness number less than 120 which comprises: providing an electrolytic cell having an anode and a cathode and a molten salt electrolyte consisting essentially of at least one alkali metal halide and at least one alkali metal fluotitanate; maintaining an inert atmosphere in said cell; charging impure titanium metal into said cell so that it is in physical contact with said anode; passing an mason-49 electrolyzing DfCJcurrent throu'ghsaid cell to deposit titanium on said cathode and to form a sludgeradj'acent during the passing of said current suflicient to deposit purified titanium metal at'the cathode but insufficient to liberate any'halogengas at the anode; maintainingthe sludge of titanium and non-metallic impurities in physical contact with said scrap;thereby separating impurities from the titanium metal and depositing refined titanium at the cathode.

3. The method of electrolytically refining impure titanium metal to produce a refined ductile metal having a Brinell hardness number less than 120 which comprises: providing an electrolytic cell having an anode and a cathode and a perforated barrier dividing said cell into an anode compartment and a cathode compartment, while permitting the circulation of a molten salt electrolyte; introducing and maintaining an inert atmosphere in said cell; forming a molten electrolyte in said cell consisting essentially of at least one alkali metal chloride and at least one alkali metal fiuotitanate; charging impure titanium metal into said cell on the anode side of said barrier so that it is in physical contact with said anode; passing a DC. electrolyzing current between said anode and cathode and through said melt, thereby depositing titanium metal at the cathode and forming a sludge containing the impurities in said metal adjacent the anode; maintaining said sludge in physical contact with the impure titanium metal charge and adjacent the anode; maintaining an anode current density and voltage during the passage of said current sufficient to deposit purified titanium metal at the cathode but insufiicient to liberate any halogen gas at the anode and insufiicient to electrolytically dissociate any of the sludge formed during said refining; thereby separating impurities from the titanium metal and depositing refined titanium at the cathode.

4. The method of electrolytically refining impure titanium metal to produce a refined ductile metal having a Brinell hardness number less than 120 which comprises: passing an electric current through an electrolytic cell having an anode and a cathode and a molten salt elec trolyte consisting essentially of at least one alkali metal chloride and at least one alkali metal fluotitanate and maintained under an inert atmosphere; charging impure titanium metal in the form of small pieces in electrical and physical contact With said anode; forming a sludge containing the impurities in said metal, by passage of said current; maintaining an anode current density and voltage during the passage of said current sufiicient to deposit purified titanium metal at the cathode but insufficient to liberate any halogen gas at the anode and insufiicient to electrolytically dissociate any of the sludge formed during said refining; intermittently compacting said metal to be refined, to cause the sludge formed during said refining to become detached from said metal and to collect on the bottom of the cell While remaining in physical contact with said impure metal; thereby separating impurities from the titanium metal and depositing refined titanium at the cathode.

5. The method of electrolytically refining impure titanium metal to produce a refined ductile metal having a Brinell hardness number less than 120 which comprises: passing an electric current through an electrolytic cell having an anode and a cathode and a molten salt electrolyte consisting essentially of sodium chloride and potassium fluotitanate (KgTiFs); disposing said impure titanium metal so that it is in physical contact with said anode and remains in physical contact with a sludge formed by the impurities during said refining; maintaining a current density and voltage during the passage of said current sufiicient to deposit purified titanium metal at the cathode but insufiicient to liberate any halogen gas at the anode, thereby depositing refined titanium at the cathode.

' 6."'The"mthod of producing a-pure "group IV-A 'me'tal'of the'g'roup consisting oftitanium, zirconium and hafnium which comprises: passing a direct electric current between an anodelin electrical contact with a source material containing said metal associated with a substantial impurity content and a cathode immersed in a fused salt electrolyte; maintaining an anode current density and a cell voltageduring the passage of said current density and a'cell voltage during the passage of said current which are sulficient'to-deposit said group 1V metal on said cathode, but insufficient to liberate any free halogen gas at the anode and insufficient to electrolytically dissociate any of the sludge formed with the impurities during said passage of current; maintaining said sludge in physical contact with said impure metal to prevent the transfer of sludge containing impurities to the cathode deposit; thereby separating the impurities from the group IV-A metal, and recovering said group IV-A metal from said cathode deposit.

7. The method of electrolytically refining an impure metal of the group consisting of impure titanium, impure zirconium and impure hafnium, to produce an electrorefined, ductile metal which comprises: passing an electrolyzing current through an electrolytic cell having an anode and a cathode and means dividing said cell into an anode compartment and a cathode compartment while permitting the circulation of a molten salt electrolyte between said compartments; introducing and maintaining an inert atmosphere in said cell; forming a molten electrolyte in said cell consisting essentially of at least one alkali metal chloride and at least one fluoride of an alkali metal and the impure metal to be refined; providing a charge comprising said impure metal and at least one additive of the group consisting of graphite and a carbide of said metal in the anode compartment of said cell and in physical contact with the anode; forming a sludge containing the impurities in said metal by passage of said current; maintaining an anode current density and voltage during the passage of said current suflicient to deposit refined metal at the cathode but insuflicient to liberate any halogen gas at the anode and insufiicient to electrolytically dissociate the sludge formed during said refining; and intermittently applying pressure to said metal to be refined to urge it into more intimate physical contact with the anode and to maintain it in physical contact with the sludge, while separating the sludge from a large portion of the surface of the small pieces constituting the charge.

8. The process of claim 7 in which the pressure is applied by tamping the pieces of charged material.

9. The process of claim 7 in which the metal recovered is titanium and the charge comprises pieces of impure titanium and pieces of graphite.

10. The process of claim 7 in which the metal to be recovered is zirconium and the charge comprises a mixture of pieces of impure zirconium and pieces of graphite.

11. In a method of electrorefining an impure metal of the group consisting of titanium, zirconium and hafnium which includes: (1) passing an electrolyzing current through an electrolytic cell circuit including an anodic portion, a cathodic portion and a molten salt electrolyte which consists essentially of at least one alkali metal halide and at least one double fluoride of an alkali metal and the metal to be electrorefined, and which connects said anodic portion to said cathodic portion; (2) disposing said impure metal so that it is in physical and electrical contact with the anodic portion of the circuit; thereby causing said impure metal to be separated into metal deposited at the cathode portion of said circuit and impurities contained in a sludge formed at the anode portion of said circuit; the improvement comprising maintaining said sludge in contact with said charge by intermittently physically urging said charge into more intimate contact with such sludge.

11 2 12. The process of claim 11 further improvedby the FOREIGN PATENTS incorporation of graphite into the i pu e charge to e 0 7 091 France 1 1955 refined- 1,105,530 France Dec. s, 1955 References Cited in the file of this patent 5 THER REFERENCES Creamer: Electrodeposition of Titanium and Zirco- UNITED STATES PATENTS nium, Wright Air Development Center, U.S.B.M., 2,734,355 Buck et a1. Feb. 14, 1956 WADC, 53-317, page 12, December 1953. 2,734,856 Schultz et a1. Feb. 14, 1956 Kroll: U.S.B.M., RI-4915, pages 1719, November 2,817,631 Gullett Dec. 24, 1957 1 1952.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,880,149 March 31, 1959 Stuart S. Carlton et a1 It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 55, for "process read proce'sses column 2, line 50, for "at at" read at all---; column 5, line 6, for "6" read .m 16 line 32, for "Brinel" read Brinell column 6, line 50, for "P" read Pb column 8, line 50, after atmosphere" strike out the comma; column 10, line 8; after "current" strike out "density"; line 9, strike out "and a cell voltage during the passage of said current -=-u Signed and sealed this 25th day of August 1959.

(SEAL) Attest:

KARL H. AXLINE I ROBERT C. WATSON Attesting Officer I Commissioner of Patents 

7. THE METHOD OF ELECTROLYTICALLY REFINING AN IMPURE METAL OF THE GROUP CONSISTING OF IMPURE TITANIUM, IMPURE ZIRCONIUM AND IMPURE HAFNIUM, TO PRODUCE AN ELECTROREFINED, DUCTILE METAL WHICH COMPRISES: PASSING AN ELECTROLYING CURRENT THROUGH AN ELECTROLYTIC CELL HAVING AN ANODE AND A CATHODE AND MEANS DIVIDING SAID CELL INTO AN ANODE COMPARTMENT AND A CATHODE COMPARTMENT WHILE PERMITTING THE CIRCULATION OF A MOLTEN SALT ELECTROLYTE BETWEEN SAID COMPARTMENTS; INTRODUCING AND MAINTAINING AN INERT ATMOSPHERE IN SAID CELL; FORMING A MOLTEN ELECTROLYTE IN SAID CELL CONSISTING ESSENTIALLY OF AT LEAST ONE ALKALI METAL CHLORIDE AND AT LEAST ONE FLUORIDE OF AN ALKALI METAL AND THE IMPURE METAL TO BE REFINED; PROVIDING A CHARGE COMPRISING SAID IMPURE METAL AND AT LEAST ONE ALKALI METAL AND GROUP CONSISTING OF GRAPHITE AND A CARBIDE OF SAID METAL IN THE ANODE COMPARTMENT OF SAID CELL AND IN PHYSICAL CONTACT WITH THE ANODE; FORMING A SLUDGE CONTAINING THE IMPURITIES IN SAID METAL BY PASSAGE OF SAID CURRENT; MAINTAINING AN ANODE CURRENT DENSITY AND VOLTAGE DURING THE PASSAGE OF SAID CURRENT SUFFICIENT TO DEPOSIT REFINED METAL AT THE CATHODE BUT INSUFFICIENT TO LIBERATE ANY HALOGEN GAS AT THE ANODE AND INSUFFICIENT TO ELECTROLYTICALLY DISSOCIATE THE SLUDGE FORMED DURING SAID REFINING; AND INTERMITTENTLY APPLYING PRESSSURE TO SAID METAL TO BE REFINED TO URGE IT INTO MORE INTIMATE PHYSICAL CONTACT WITH THE SLUDGE, WHILE TO MAINTAIN IT IN PHYSICAL CONTACT WITH THE SLUDGE, WHILE SEPARATING THE SLUDGE FROM A LARGE PORTION OF THE SURFACE OF THE SMALL PIECES CONSTITUTING THE CHARGE. 